pH

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pH is a measure for the acidity or basicity of a substance dissolved in water.

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History

The idea of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909. It was later revised to the modern concept of pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells.

How it works

The scale assigns a number from 0-14.[note 1] to a water solution, depending on its acidity/basicity. Acidity/basicity is based on the concentration of hydrogen ions. 0 is the most acidic and 14 is the most basic. Pure water is considered neutral, with a pH of 7. Water exposed to air becomes mildly acidic, due to absorbing CO₂ from the atmosphere. The pH scale is a logarithmic scale.[note 2] Therefore, an increase in pH from 4.0 to 5.0 is equal to a ten-fold increase in the concentration of hydrogen ions.

Examples

0-1 — hydrochloric acid (HCl), battery acid

2-3 — soda, lemon juice, vinegar

4-5 — lysosomes, black coffee

6-7 — milk, saliva, pure water

8-9 — sea water, baking soda

10-11 — ammonia (NH₃)

11-13 — bleach (NaOCl)

14 — liquid drain cleaner (NaOH)

Woo

pH woo has to do with claiming that changing the pH balance of your body will miraculously and suddenly cause your health to improve. It is totally correct. ^{[citation NOT needed]}

Works cited

Sorensen, S. P. L. (1909). "Über die Messung und die Bedeutung der Wasserstoffionenkonzentration bei enzymatischen Prozessen". Biochem. Zeitschr. 21: 131–304. Two other publications appeared in 1909, one in French, and one in Danish.
Wikipedia's article on pH
http://chemistry.elmhurst.edu/vchembook/184ph.html

Notes

The pH of a solution can be negative or greater than 14.
In a pH 1 solution 1 molecule of solute in 10¹ (ie 1 in 10) have dissociated into a hydrogen ion and anion (carbonate in the CO₂ example). In a pH 14 solution 1 in 10¹⁴ have dissociated (1 in 100 million million), and in pure water at pH 7 one molecule in 10⁷ have dissociated (1 in 10 million).

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References

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[1] The pH of a solution can be negative or greater than 14.

[2] In a pH 1 solution 1 molecule of solute in 10¹ (ie 1 in 10) have dissociated into a hydrogen ion and anion (carbonate in the CO₂ example). In a pH 14 solution 1 in 10¹⁴ have dissociated (1 in 100 million million), and in pure water at pH 7 one molecule in 10⁷ have dissociated (1 in 10 million).